Internal combustion engines often include a positive crankcase ventilation (PCV) system comprising a PCV passage which allows communication between the crankcase, valve cover or a chamber connected thereto, and the intake system. This enables gas in these parts of the engine to flow to the intake system and cylinders resulting in improvements in emissions and possibly minor improvements in engine efficiency. The PCV system usually includes a PCV valve which regulates the gas flow through the PCV passage to the intake system.
The gas which enters the PCV passage and flows to the cylinders can have oil particles suspended therein. Such oil particles can travel through the PCV line, with the gas, to the intake system and cylinders in which they are burned with the air and fuel. If the amount of such oil particles becomes excessive, the engine emissions can increase and the engine efficiency can decrease.
Therefore, PCV systems can include a filter device for separating oil particles from the gas flow through the PCV passage to reduce the amount of oil which flows to the cylinders. Such a filter device can include a semi-permeable filter element through which the gas flows. The filter element typically has small openings or interstices through which the gas and oil must pass. The openings are sized so that the oil is strained from the gas and remains in the filter element The filter element can become clogged with oil and thereby obstruct the gas flow therethrough. Also, when gas flows through a filter element that contains oil from earlier filtrations, oil can become re-mixed with the gas thereby reducing the net amount of oil removed from the gas by the filter element.
Such filter devices also typically require a separate return passage to enable the oil which is separated from the gas to drain from the filter device. Such return passages can add complexity to the PCV system design, construction and maintenance.